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Networking

Networking. Basic network components and layered architecture Internet and WWW basics IP, TCP, URL, HTTP. Jean Walrand, Communication Networks, a first course, McGraw-Hill 1998 (2 nd edition). Types of computer networks:. Point-to-point connection (link) between two computers

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Networking

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  1. Networking • Basic network components and layered architecture • Internet and WWW basics • IP, TCP, URL, HTTP Jean Walrand, Communication Networks, a first course, McGraw-Hill 1998 (2nd edition). CSCI 1106, Fall 2008

  2. Types of computer networks: • Point-to-point connection (link) between two computers • Store-and-forward transmission: packets • Datagram packet switching: destination address in packet • also, LAN, WAN, ATM (virtual circuit switching), wireless e.g. PPP, SLIP A B C e.g. token ring CSCI 1106, Fall 2008

  3. multiple access networks (e.g. ALOHA, Ethernet) CSCI 1106, Fall 2008

  4. CSCI 1106, Fall 2008

  5. CSCI 1106, Fall 2008

  6. CSCI 1106, Fall 2008

  7. CSCI 1106, Fall 2008

  8. Review of components • Hosts • Considered a “node” or “end point” in the network (client/server/printer) • Processes all levels of the protocol stack • Hubs • acts as an “extender” - similar in effect to taking all incoming lines and twisting the wires together • Does not do any processing - acts only at the physical layer • Bridges • attaches two physically identical LANs together, physical layer processing • forwards only traffic which is destined for “the other side” • Switches • depending on level of switch complexity, anywhere from a hub to a router • Routers • Processing at the Network layer • Route packets between networks with potentially different lower level protocol stacks (i.e., different physical and data link layers) • Gateways • Processes all levels of the protocol stack • Used to connect networks with different protocol stacks CSCI 1106, Fall 2008

  9. Layered communication model Message received Message sent Layer n Layer 2 Layer 1 Communication Sender Recipient medium Coulouris, Dollimore, Kindberg, Distributed Systems, Addison Wesley 2001 (3rd ed) CSCI 1106, Fall 2008

  10. ISO-OSI layer model Open systems interconnection reference model A B communication services communication services, e.g. file transfer, email, … 7. 7. Application local syntax, secure, efficient connections e.g. compression, security, format conversion 6. 6. Presentation connections 5. 5. supervises connections between end systems Session delivery of messages 4. 4. supervises end-to-end transmission Transport 3. 3. guides the packet from source to destinations Network implements packet delivery service between two nodes on the same physical link 2. 2. Data Link 1. 1. Physical Implements digital communication link that delivers bits CSCI 1106, Fall 2008

  11. Layer Description Examples Application Protocols that are designed to meet the communication requirements of FTP HTTP, , SMTP, specific applications, often defining the interface to a service. CORBA IIOP Presentation Protocols at this level transmit data in a network representation that is Secure Sockets independent of the representations used in individual computers, which may ( SSL),CORBA Data differ. Encryption is also performed in this layer, if required. Rep. Session At this level reliability and adaptation are performed, such as detection of failures and automatic recovery. Transport This is the lowest level at which messages (rather than packets) are handled. TCP, UDP Messages are addressed to communication ports attached to processes, Protocols in this layer may be connection-oriented or connectionless. Network Transfers data packets between computers in a specific network. In a WAN IP, ATM virtual or an internetwork this involves the generation of a route passing through circuits routers. In a single LAN no routing is required. Data link Responsible for transmission of packets between nodes that are directly Ethernet MAC, connected by a physical link. In a WAN transmission is between pairs of ATM cell transfer, routers or between routers and hosts. In a LAN it is between any pair of hosts. PPP Physical The circuits and hardware that drive the network. It transmits sequences of Ethernet base- band binary data by analogue signalling, using amplitude or frequency modulation signalling, ISDN of electrical signals (on cable circuits), light signals (on fibre optic circuits) or other electromagnetic signals (on radio and microwave circuits). CSCI 1106, Fall 2008

  12. What is a protocol `A protocol is a set of rules governing message interchanges which occur between a number of computers in a distributed system; each of these messages implement functions of the system. A protocol is also used to establish a connection and allow entities to exchange data about themselves, for example the operating system they are using and the format of the data that they intend passing; this is known as a handshake. ‘ D. Ince CSCI 1106, Fall 2008

  13. CSCI 1106, Fall 2008

  14. Application message port TCP header TCP IP header Ethernet header IP Ethernet frame CSCI 1106, Fall 2008

  15. IP Header CSCI 1106, Fall 2008

  16. Around 4 billion IP addresses CSCI 1106, Fall 2008

  17. Transport layer protocols • TCP (Transmission Control Protocol): • connection-oriented • Reliable packet delivery in sequence • UDP (User Datagram Protocol): • connectionless (datagram) • Unreliable packet delivery • Packets may arrive out of sequence or duplicated • Less overhead • Simply adds port addressing to IP • Checksum is optional • Internet Control Message Protocol • Used by the nodes in the internet to implement IP CSCI 1106, Fall 2008

  18. TCP and UDP Header CSCI 1106, Fall 2008

  19. CSCI 1106, Fall 2008

  20. The Internet around 1990 Jean Walrand, Communication Networks, a first course, McGraw-Hill 1998 (2nd edition). The first three chapters give you a nice overview of the working of networks and the Internet. CSCI 1106, Fall 2008

  21. MCI backbone Retrieved from: http://global.mci.com/about/network/maps/?flash=1&theme=/, Sept 5/2003 See this site also for interesting network statistics (e.g. latencies) CSCI 1106, Fall 2008

  22. ISP ISP ISP ISP NAP NAP ISP ISP NAP NAP ISP Backbone ISP ISP ISP Network Service Provider Internet Service Provider Private Networks / hosts Internet network architecture Adapted from Electronic Commerce: A Managerial Perspective. Turban, Lee, King and Chung, 2000. Pg. 385 CSCI 1106, Fall 2008

  23. b.atr.go.jp a.cs.dal.ca CSCI 1106, Fall 2008

  24. URL: A Global Address • Scheme • Server name • Path • File http://www.cs.dal.ca/cs1200/week1/x.html CSCI 1106, Fall 2008

  25. b.atr.go.jp a.cs.dal.ca 123.777.19.6 168.12.13.3 CSCI 1106, Fall 2008

  26. Routing and congestion control • Send information of nodes and links to each node of the network. This might include some physical properties such as maximal size of packets, typical time delays, … • Build map of network • Use routing algorithm to build routing tables for example: OSPF (Open Shortest Path First) if every router uses the same algorithm and maps they build consistent tables • Hierarchical Routing: `use local map to get to the highway, use highway map to get to your destination town, use local map to get to your friends house’. More sophisticated routing on `highway’ (BGP, Border Gateway Protocol) How is congestion controlled? CSCI 1106, Fall 2008

  27. How is congestion controlled? Flow control  TCP Destination publishes maximal acceptable window size in reply message Source destination discovers congestion from unusually long delay times of response  additive increase, multiplicative decrease CSCI 1106, Fall 2008

  28. Application layer:Programming example in Java The JAVA Socket class Socket oldSock = new Socket("penny.open.ac.uk", 1048); remote computer penny in the domain open.ac.uk with communication occurring via port 1048. InputStream CSCI 1106, Fall 2008

  29. Network (internet) applications WWW & Semantic Web CSCI 1106, Fall 2008

  30. Tim Berners-Lee CSCI 1106, Fall 2008

  31. World Wide Web Internet Web server Borg Public_html Index.html • Parts of the puzzle • URL • HTTP • HTML Web browser Your Machine CSCI 1106, Fall 2008

  32. HTTP: Hyper Text Transfer Protocol • Lightweight protocol that browsers and servers use to communicate with one another • On top of (in the application layer of) the TCP/IP model • HTTP session begins when a client’s browser requests a Web page. Once the server responds by sending the page requested, the HTTP session ends CSCI 1106, Fall 2008

  33. client request: GET /index.html HTTP/1.1User-Agent: Lynx/2.4Connection: Keep-AliveHost: www.openaccess.comAccept: text/html Server response: HTTP/1.1 200 OKDate: Thu, 22 July 1998 18:40:55 GMTServer: Apache 1.3.5 (Unix) PHP/3.0.6Last-Modified: Mon, 19 July 1997 16:03:22 GMTContent-Type: text/htmlContent-Length: 12987... MIME type (Multipurpose Internet Mail Extension) CSCI 1106, Fall 2008

  34. HTTP is stateless!!! • stateless because every request that a browser makes opens a new connection that is immediately closed after the document is returned • even a web page with many objects (graphics, sound, video, etc) requires separate HTTP requests for each object • each operation is unaware of any other connection • the server cannot maintain state information about successive requests easily CSCI 1106, Fall 2008

  35. Web client/server communication • Like any other client/server application, web browsers and servers need a way to: • Locate each other so they can send requests and responses back and forth • Uniform Resource Locator (URL) • Communicate with one another • Hypertext Transport Protocols (HTTP) (See networking section) CSCI 1106, Fall 2008

  36. Interactivity • HTML is a presentation language – not a programming language • controls the appearance of the information on the client’s screen but does not support processing or manipulating information • early web browsers were limited to displaying static pages • But … many business applications require interactivity  Client-side & server-side processing CSCI 1106, Fall 2008

  37. TML (XML) <thomas> <lecture type=‘early’> <opening> Guten Morgen </opening> <message> bla bla </message> <lecture> <research> <paper> </paper> </research> </thomas> CSCI 1106, Fall 2008

  38. DTD <!ELEMENT ele_name (list of child elements +*?)> Leaf element: <!ELEMENT name (#PCDATA)> <!ATTLIST ele_name att_name att_type att_value> <!ENTITY ent_name “ent_value”> CSCI 1106, Fall 2008

  39. DTD XML Document XML Parser & Syntax Validator valid / not valid DTD Document For example MSXML CSCI 1106, Fall 2008

  40. XSLT XML Document XSLT Processor XML Document XSLT Document CSCI 1106, Fall 2008

  41. XSLT Include in XML document <?xml-stylesheet type=“text/xsl” href=“URL” ?> XSLT document: <xsl:stylesheet version = “1.0” xmlns:xsl = “url of xslt” xmlns = “url of xhtml”> <xsl:templates match = “root”> <html> <head> </head> <body> <h1> ….. <xsl:for-each select = “tag”> <span style =“ whatever”> message </span> <xsl:value-of select = “subtag” /> <other html tags> …. </xsl:for-each> </html> </xsl:template> </xsl:stylesheet> CSCI 1106, Fall 2008

  42. Tim Berners-Lee CSCI 1106, Fall 2008

  43. Web Hub • Content Management Console Google News Admin XML Content Repository Retrieve General Public Modify Control Panel Front End Site P u b l i c Modify Database Member’s Section Alumni CSCI 1106, Fall 2008

  44. Web service architecture http://www.w3.org/2002/ws/ Adopted from Clabby, 2002 CSCI 1106, Fall 2008

  45. SOAP • Simple Object Access Protocol • XML-based protocol • Exchange of information between applications over HTTP • Seems to become the widely accepted solution to electronic data interchange (EDI) and remote procedure call (RPC, CORBA, etc) http://www.w3.org/TR/soap12-part0/ CSCI 1106, Fall 2008

  46. Semantic Web stack CSCI 1106, Fall 2008

  47. From http://www.w3.org/2001/sw/ Semantic Web The Semantic Web provides a common framework that allows data to be shared and reused across application, enterprise, and community boundaries. It is a collaborative effort led by W3C with participation from a large number of researchers and industrial partners. It is based on the Resource Description Framework (RDF), which integrates a variety of applications using XML for syntax and URIs for naming. "The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in cooperation." -- Tim Berners-Lee, James Hendler, Ora Lassila, The Semantic Web, Scientific American, May 2001 CSCI 1106, Fall 2008

  48. Create meaning for automated processing: intelligent agents RDF: (Web) Resource Description Framework http://www.w3.org/TR/rdf-primer/ Web Ontology: OWL http://www.w3.org/TR/owl-features/ Standardized Query Language: SPARQL Simple example: [Really Simple Syndication (RSS 2.0)] RDF Site Summary (RSS 1.0 and RSS 0.90) Rich Site Summary (RSS 0.91) CSCI 1106, Fall 2008

  49. Intro videos Semantic Web: http://www.youtube.com/watch?v=OGg8A2zfWKg RDF: http://www.youtube.com/watch?v=ldl0m-5zLz4 CSCI 1106, Fall 2008

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